Abstract
The aim of current study was to determine the recycled concrete aggregate (RCA) applicability in the production of concrete mixture for vibropressed concrete blocks. The experiments were focused especially on the crushed waste material from the same concrete elements producing plant. For this type of precast elements only some finer fractions can be implemented and the “earth-moist” consistency of fresh mixture is required. The series of samples was prepared in which the mixture of natural aggregates was partially or totally substituted by recycled concrete aggregate. The 0/4 RCA fraction, which is usually rejected in ready mix concrete technology, plays a role of 0/2 sand. The substitution of sand fraction was from 20% to 100% respectively. The substitution of the coarser aggregate fractions by 4/16 RCA was also done. The standard properties of vibropressed elements, such as the degree of densification, the density of material, the compressive and splitting tensile strength and the water absorption capacity according to the relevant standards were determined. The parameters of materials with the natural aggregate substitution by RCA are affected by the ratio of recycled concrete aggregate. In most cases the results do not decline specially from those for reference samples, when only the natural sand (0/2) fraction is substituted by the 0/4 recycled aggregate. As one could expect, as lower the substitution, as better the test results. The partial substitution of natural aggregate by coarser fractions requires experimental verification; over 20% substitution of natural aggregate by 4/8, 8/16 or 0/16 RCA should be excluded.
Highlights
The production of concrete small vibropressed elements has been bound first of all to the development of modern urban road infrastructure
One should take in mind that in concrete mixtures used to produce the vibropressed non-construction concrete materials the recycled aggregate fraction 0/4, which is usually rejected in ready mix concrete technology, can successfully replace the 0/2 natural sand fraction
The three samples of crushed concrete paving blocks from the vibropressed concrete paving blocks producing plant were taken as recycled aggregate: 1) The recycled concrete aggregate (RCA) 0/16 obtained by simple one-step crushing and sieving, 2) The recycled concrete aggregate (RCA) fraction 4/16, 3) The recycled concrete aggregate (RCA) fraction 0/4, The aggregate fractions are presented in fig. 1
Summary
The production of concrete small vibropressed elements has been bound first of all to the development of modern urban road infrastructure. In the experiments the “in situ” wastes from the concrete blocks producing plants were taken into account with the same other materials, such as cement, aggregate and admixtures used in current production. One should take in mind that in concrete mixtures used to produce the vibropressed non-construction concrete materials the recycled aggregate fraction 0/4, which is usually rejected in ready mix concrete technology, can successfully replace the 0/2 natural sand fraction. This is of importance because of the preservation of natural sand used as a raw material in many building materials production. The production of concrete mixture used in the vibropressed precast concrete technology
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